1. Field of the Invention
The present invention relates to a printing unit comprising a first roller and a second roller provided substantially parallel and facing each other for transport of printing sheets between the rollers. The rollers have substantially parallel rotation axes for transport of printing sheets between the first roller and the second roller by abutting the printing sheets from either side or for transfer of liquid from one to the other of the first roller and the second roller by abutment of the first roller to the second roller. The first roller is rotationally mounted to a deflector at only one end of the first roller. The deflector comprises a connection to a support, by which the parallel orientation can be adjusted as well as the contact pressure between the rollers. The invention also comprises a method for adjusting the angle between two rollers in a printing unit.
2. Description of Related Art
In flexographic printing presses, mounting of printing rollers at only one end is attractive when used with sleeves, because the exchange of such sleeve is easier than in presses where the rollers are mounted at both ends. However, the mounting of the rollers at only one end implies a challenge with respect to suitable adjustment mechanisms by which a parallel contact and equalized pressure between the rollers is assured in order to provide uniform transfer of ink between the rollers.
U.S. Pat. No. 5,385,093 by Rogge assigned to Windmoeller and Hoelscher discloses an inking unit with a cantilevered inking roller and plate cylinder, which both are mounted only at one end. In order to achieve parallel adjustment between the inking roller and the plate cylinder and in order to achieve uniform contact pressure between the rollers, the inking unit has a cantilevered mount of the plate cylinder. This mount comprises an arrangement, wherein a screw pushes on one side of a lever, the rotation of which moves a pin in a groove. The groove allows a free motion of the pin in one dimension, but not in the lateral direction; instead, the lateral direction of the pin causes the pin to push onto the plate cylinder block, causing a rotation of the plate cylinder block around a further rotation pin. The rotation of the plate cylinder block causes rotation of the plate cylinder axle and thereby adjusts the angle between the plate cylinder and the inking roller.
This system is rather complicated due to its many rotational parts. For example, the screw is engaged in a bearing on the lever, the bearing is rotating in the lever about a first rotational axis, the lever is rotating about a second rotating axis, and the plate cylinder block is rotating about a third rotating axis. Likewise, three rotational axes are used for the inking roller block when it has to be adjusted together with the plate cylinder against an impression cylinder. The many rotational parts and the relatively complicated interplay between the rotational parts, pins, and grooves make the system difficult, heavy and expensive in fabrication.
Other systems for adjusting printing rollers that are mounted in only one end are disclosed in U.S. Pat. No. 6,109,180 by Guaraldi et al. and in U.S. Pat. No. 5,471,929 by Rogge. An offset printing machine with rollers that can be adjusted is disclosed in UK Patent Application GB 2 142 577 A by Atkinson. An elastic element for mounting printing units is disclosed in European Patent Application EP 0 942 192 A1.